XML文档解析 : doc/sax

dom和sax解析方式的区别：
1.dom解析的优点是对文档的crud比较方便，缺点是占用内存比较大
2.sax解析的优点是占用内存少，解析速度快，缺点是只适合做文档的读取，不适合做文档的crud。

调整jvm大小（默认64M）：
-Xmx80m

//使用dom方式对xml进行crud

//使用dom方式对xml进行crud
public class demo3 {
    //得到xml文档中的标签
    @Test
    public void read1() throws Exception
    {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = factory.newDocumentBuilder();
        Document doc = db.parse("src/book.xml");

        NodeList nl =  doc.getElementsByTagName("title");
        Node node = nl.item(0);     
        String content1 =  node.getNodeName();

        System.out.println(content1);
    }
    //得到xml文档中所有标签
    @Test
    public void read2() throws Exception
    {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse("src/book.xml");

        NodeList ll = doc.getElementsByTagName("booklist");

        Node node = ll.item(0);
        List(node);

    }
    private void List(Node node) 
    {
        if(node instanceof Element )
        {
            System.out.println(node.getNodeName());
        }
        NodeList nl = node.getChildNodes();
        for(int i =0; i<nl.getLength();i++)
        {
            Node nod = nl.item(i);
            List(nod);
        }
    }
    //得到xml文档中标签属性的值<书名 id="a1">中的a1
    @Test
    public void read3() throws Exception
    {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse("src/book.xml");

        Node node = doc.getElementsByTagName("title").item(0);
        Element el = (Element)node;
        System.out.println(el.getAttribute("id"));
    }

}